1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of forming a floating gate in a flash memory device by which the floating gate is formed in the self-aligned mode.
2. Background of the Related Art
Recently, as the design rule is reduced and the size of the device is reduced, it is difficult to control overlapping of a field oxide film (FOX) that has the greatest influence on the distance between the floating gates and coupling in the ETOX (EEPROM tunnel oxide) cell. In general, the flash memory cell is implemented using the STI process. Upon isolation of the floating gate, the uniformity of the wafer depending on variation of the critical dimension (CD) is not easy in the patterning process using the mask. For this reason, there is a problem that the coupling ratio between the devices is not uniform. Furthermore, if a high bias voltage is applied during the programming or erasing operation of the flash memory devices, defective flash memory devices may occur due to a uniform floating gate. In addition, the production yield is degraded and the cost price is increased, due to misalignment between the isolation mask and the poly mask and an increased mask process.